Cascade heat transfer system

ABSTRACT

A transport refrigeration system (TRS) includes a first heat transfer circuit including a first compressor, a condenser, a first expansion device, and a cascade heat exchanger. The first compressor, the condenser, the first expansion device, and the cascade heat exchanger are in fluid communication such that a first heat transfer fluid can flow therethrough. The TRS includes a second heat transfer circuit including a second compressor, the cascade heat exchanger, a second expansion device, and an evaporator. The second compressor, the cascade heat exchanger, the second expansion device, and the evaporator are in fluid communication such that a second heat transfer fluid can flow therethrough. The first heat transfer circuit and the second heat transfer circuit are arranged in thermal communication at the cascade heat exchanger such that the first heat transfer fluid and the second heat transfer fluid are in a heat exchange relationship at the cascade heat exchanger.

FIELD

This disclosure relates generally to a transport refrigeration system(TRS), More specifically, the disclosure relates to systems and methodsfor providing a cascade heat exchange between a plurality of heattransfer circuits in a TRS.

BACKGROUND

A transport refrigeration system (TRS) is generally used to control oneor more environmental conditions such as, but not limited to,temperature, humidity, and/or air quality of a transport unit. Examplesof transport units include, but are not limited to, a container (e.g., acontainer on a flat car, an intermodal container, etc.), a truck, aboxcar, or other similar transport units. A refrigerated transport unitis commonly used to transport perishable items such as produce, frozenfoods, and meat products. Generally, the refrigerated transport unitincludes a transport unit and a TRS. The TRS includes a transportrefrigeration unit (TRU) that is attached to the transport unit tocontrol one or more environmental conditions (e.g., temperature,humidity, etc.) of a particular space (e.g., a cargo space, a passengerspace, etc.) (generally referred to as a “conditioned space”). The TRUcan include, without limitation, a compressor, a condenser, an expansiondevice, an evaporator, and one or more fans or blowers to control theheat exchange between the air inside the conditioned space and theambient air outside of the refrigerated transport unit.

SUMMARY

This disclosure relates generally to a transport refrigeration system(TRS). More specifically, the disclosure relates to systems and methodsfor providing a cascade heat exchange between a plurality of heattransfer circuits in a TRS.

In an embodiment, the TRS includes a first heat transfer circuit and asecond heat transfer circuit in thermal communication. In an embodimentthe first heat transfer circuit includes a relatively low global warmingpotential (GWP) heat transfer fluid and the second heat transfer circuitincludes a heat transfer fluid that is carbon dioxide (CO₂, alsoreferred to as R-744).

In an embodiment, a heat transfer fluid having a relatively low GWPincludes, but is not limited to, unsaturated hydrofluorocarbons (HFCs)such as hydrofluoroolefins (HFOs), hydrocarbons (HCs), ammonia, andcarbon dioxide (R-744).

A transport refrigeration system (TRS) is described. The TRS includes afirst heat transfer circuit including a first compressor, a condenser, afirst expansion device, and a cascade heat exchanger. The firstcompressor, the condenser, the first expansion device, and the cascadeheat exchanger are in fluid communication such that a first heattransfer fluid can flow therethrough. The TRS includes a second heattransfer circuit including a second compressor, the cascade heatexchanger, a second expansion device, and an evaporator. The secondcompressor, the cascade heat exchanger, the second expansion device, andthe evaporator are in fluid communication such that a second heattransfer fluid can flow therethrough. The first heat transfer circuitand the second heat transfer circuit are arranged in thermalcommunication at the cascade heat exchanger such that the first heattransfer fluid and the second heat transfer fluid are in a heat exchangerelationship at the cascade heat exchanger.

A system is also disclosed. The system includes an internal combustionengine; a first heat transfer circuit, and a second heat transfercircuit. The first heat transfer circuit includes a first compressor, acondenser, a first expansion device, and a cascade heat exchanger,wherein the first compressor, the condenser, the first expansion device,and the cascade heat exchanger are in fluid communication such that afirst heat transfer fluid can flow therethrough. The second heattransfer circuit includes a second compressor, the cascade heatexchanger, a second expansion device, and an evaporator, wherein thesecond compressor, the cascade heat exchanger, the second expansiondevice, and the evaporator are in fluid communication such that a secondheat transfer fluid can flow therethrough. The first heat transfercircuit and the second heat transfer circuit are arranged in thermalcommunication at the cascade heat exchanger such that the first heattransfer fluid and the second heat transfer fluid are in a heat exchangerelationship at the cascade heat exchanger.

A method of heat transfer in a transport refrigeration system (TRS) isalso disclosed. The method includes providing a first heat transfercircuit including a first compressor, a condenser, a first expansiondevice, and a cascade heat exchanger, wherein the first compressor, thecondenser, the first expansion device, and the cascade heat exchangerare in fluid communication such that a first heat transfer fluid canflow therethrough, and a second heat transfer circuit, including asecond compressor, the cascade heat exchanger, a second expansiondevice, and an evaporator, wherein the second compressor, the cascadeheat exchanger, the second expansion device, and the evaporator are influid communication such that a second heat transfer fluid can flowtherethrough. The method further includes disposing the first heattransfer circuit and the second heat transfer circuit in thermalcommunication at the cascade heat exchanger such that the first heattransfer fluid and the second heat transfer fluid are in a heat exchangerelationship at the cascade heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

References are made to the accompanying drawings that form a part ofthis disclosure, and which illustrate embodiments in which the systemsand methods described in this specification can be practiced.

FIG. 1 illustrates a side view of a refrigerated transport unit,according to an embodiment.

FIG. 2 is a schematic diagram of a heat transfer system for a transportrefrigeration system, according to an embodiment.

FIG. 3A is a schematic diagram of a reverse cycle heating/defrostcircuit for the heat transfer system of FIG. 2 for a transportrefrigeration system, according to an embodiment.

FIG. 3B is a schematic diagram of a hot gas bypass heating/defrostcircuit for the heat transfer system of FIG. 2 for a transportrefrigeration system, according to an embodiment.

FIG. 4A is a schematic diagram of a heat transfer system for a transportrefrigeration system, according to an embodiment.

FIG. 4B is a schematic diagram of a heat transfer system for a transportrefrigeration system, according to an embodiment.

Like reference numbers represent like parts throughout.

DETAILED DESCRIPTION

This disclosure relates generally to a transport refrigeration system(TRS). More specifically, the disclosure relates to systems and methodsfor providing a cascade heat exchange between a plurality of heattransfer circuits in a TRS.

A TRS is generally used to control one or more environmental conditionssuch as, but not limited to, temperature, humidity, and/or air qualityof a transport unit. Examples of transport units include, but are notlimited to, a container (e.g., a container on a flat car, an intermodalcontainer, etc.), a truck, a boxcar, or other similar transport units. Arefrigerated transport unit (e.g., a transport unit including a TRS) canbe used to transport perishable items such as, but not limited to,produce, frozen foods, and meat products.

As disclosed in this specification, a TRS can include a transportrefrigeration unit (TRU) which is attached to a transport unit tocontrol one or more environmental conditions (e.g., temperature,humidity, air quality, etc.) of an interior space of the refrigeratedtransport unit. The TRU can include, without limitation, a compressor, acondenser, an expansion valve, an evaporator, and one or more fans orblowers to control the heat exchange between the air within the interiorspace and the ambient air outside of the refrigerated transport unit.

A “transport unit” includes, for example, a container (e.g., a containeron a flat car, an intermodal container, etc.), truck, a boxcar, or othersimilar transport unit.

A “transport refrigeration system” (TRS) includes, for example, arefrigeration system for controlling the refrigeration of an interiorspace of a refrigerated transport unit. The TRS may include avapor-compressor type refrigeration system, a thermal accumulator typesystem, or any other suitable refrigeration system that can userefrigerant, cold plate technology, or the like.

A “refrigerated transport unit” includes, for example, a transport unithaving a TRS.

Embodiments of this disclosure may be used in any suitableenvironmentally controlled transport apparatus, such as, but not limitedto, a shipboard container, an air cargo cabin, and an over the roadtruck cabin.

Generally, a TRS may use hydrofluorocarbon (HFC) heat transfer fluids(commonly referred to as a “refrigerant”). For example, one commonlyused HFC heat transfer fluid is R-404A (as identified according to itsAmerican Society of Heating, Refrigerating, and Air ConditioningEngineers (“ASHRAE”) designation). The R-404A heat transfer fluid,however, has a relatively high global warming potential (GWP). The GWPof R-404A is 3,922 (on the 100 year GWP time horizon, according to theIntergovernmental Panel on Climate Change (IPCC Report 4)).

An increasing focus is being placed on replacing the HFC heat transferfluids with relatively lower GWP alternatives. Examples of suitablealternatives include, but are not limited to, unsaturated HFCs such ashydrofluoroolefins (HFOs), hydrocarbons (HCs), ammonia, and carbondioxide (CO₂, also known by its ASHRAE designation of R-744). Carbondioxide, for example, has a GWP of 1. These alternatives have a varietyof advantages and disadvantages such as, for example, safety risks(e.g., flammability, operating pressure, etc.), thermophysicalproperties (e.g., relating to efficiency of the TRS), cost,availability, or the like. In general, embodiments described herein canreduce global warming impact due to emissions of the heat transfer fluidinto the environment, optimize efficiency of the TRS and reduce anamount of energy input to maintain a desired condition in a conditionedspace, or the like.

FIG. 1 illustrates a side view of a TRS 100 for a transport unit 125,according to an embodiment. The illustrated transport unit 125 is atrailer-type transport unit. Embodiments as described in thisspecification can be used with other types of transport units. Forexample, the transport unit 125 can represent a container (e.g., acontainer on a flat car, an intermodal container, etc.), a truck, aboxcar, or other similar type of refrigerated transport unit includingan environmentally controlled interior space.

The TRS 100 is configured to control one or more environmentalconditions such as, but not limited to, temperature, humidity, and/orair quality of an interior space 150 of the transport unit 125. In anembodiment, the interior space 150 can alternatively be referred to asthe conditioned space 150, the cargo space 150, the environmentallycontrolled space 150, or the like. In particular, the TRS 100 isconfigured to transfer heat between the air inside the interior space150 and the ambient air outside of the transport unit 125.

The interior space 150 can include one or more partitions or internalwalls (not shown) for at least partially dividing the interior space 150into a plurality of zones or compartments, according to an embodiment.It is to be appreciated that the interior space 150 may be divided intoany number of zones and in any configuration that is suitable forrefrigeration of the different zones. In some examples, each of thezones can have a set point temperature that is the same or differentfrom one another.

The TRS 100 includes a transport refrigeration unit (TRU) 110. The TRU110 is provided on a front wall 130 of the transport unit 125. The TRU110 can include a prime mover (e.g., an internal combustion engine) (notshown) that provides power to a component (e.g., a compressor, etc.) ofthe TRS 100.

The TRU 110 includes a programmable TRS Controller 135 that includes asingle integrated control unit 140. It is to be appreciated that, in anembodiment, The TRS controller 135 may include a distributed network ofTRS control elements (not shown). The number of distributed controlelements in a given network can depend upon the particular applicationof the principles described in this specification. The TRS Controller135 can include a processor, a memory, a clock, and an input/output(I/O) interface (not shown). The TRS Controller 135 can include fewer oradditional components.

The TRU 110 also includes a heat transfer circuit (as shown anddescribed in FIG. 2). Generally, the TRS Controller 135 is configured tocontrol a heat transfer cycle (e.g., controlling the heat transfercircuit of the TRU 110) of the TRS 100. In one example, the TRSController 135 controls the heat transfer cycle of the TRS 100 to obtainvarious operating conditions (e.g., temperature, humidity, air qualityetc.) of the interior space 150.

FIG. 2 is a schematic diagram of a heat transfer system 200 for a TRS(e.g., the TRS 100 of FIG. 1), according to an embodiment. The heattransfer system 200 includes a first heat transfer circuit 205 and asecond heat transfer circuit 210. In an embodiment, the first heattransfer circuit 205 can alternatively be referred to as the primaryheat transfer circuit 205, the high side heat transfer circuit 205, thecondensing side heat transfer circuit 205, the stage two heat transfercircuit, or the like. In an embodiment, the second heat transfer circuit210 can alternatively be referred to as the low side heat transfercircuit 210, the evaporating side heat transfer circuit 210, or thelike. The first heat transfer circuit 205 is in thermal communicationwith the second heat transfer circuit 210.

The first heat transfer circuit 205 includes a compressor 220, acondenser 230, a condenser fan 235, a first accumulator 240, a heatexchanger 245, an expansion device 250, a cascade heat exchanger 255,and a second accumulator 260. The compressor 220, condenser 230, firstaccumulator 240, heat exchanger 245, expansion device 250, cascade heatexchanger 255, and second accumulator 260 are fluidly connected to formthe first heat transfer circuit 205 in which a heat transfer fluid cancirculate therethrough. The heat transfer fluid can generally be a heattransfer fluid having a relatively low global warming potential (GWP).Examples of suitable heat transfer fluids for the first heat transfercircuit 205 can include, but are not limited to, hydrofluoroolefins(HFOs), hydrocarbons (HCs), and carbon dioxide (CO₂) (also known by itsASHRAE Standard 34 designation R-744), or the like.

In the illustrated embodiment, the compressor 220 is driven by a powersource 215. The power source 215 can be, for example, a part of the TRU110 (FIG. 1). The power source 215 (e.g., an internal combustion engine,an electric drive motor, etc.) can provide mechanical power directly tothe compressor 220. The power source 215 can also provide mechanicalpower directly to a generator (e.g., an alternator, etc.), which can beused to provide power either to the compressor 220 or a secondcompressor 275 of the second heat transfer circuit 210. In such anembodiment, the power source 215 may include a converter between thegenerator and the second compressor 275 to provide an appropriate powersource for the second compressor 275. In an embodiment in which thepower source 215 includes an electric drive motor that providesmechanical power directly to the compressor 220 and/or the secondcompressor 275, the electric power can come from any of a variety ofsources (e.g., batteries, shore power, etc.).

The second heat transfer circuit 210 includes the second compressor 275,the cascade heat exchanger 255, a third accumulator 280, a secondexpansion device 285, an evaporator 290, and an evaporator fan 295. Thesecond compressor 275, cascade heat exchanger 255, third accumulator280, second expansion device 285, and evaporator 290 are fluidlyconnected to form the second heat transfer circuit 210 in which a heattransfer fluid can circulate therethrough. The heat transfer fluid inthe second heat transfer circuit 210 can generally be different from theheat transfer fluid in the first heat transfer circuit 205. The heattransfer fluid in the second heat transfer circuit 210 can be, forexample, R-744 (CO₂). The heat transfer fluid in the second heattransfer circuit 210 can be selected, for example, based on itsperformance at relatively low temperatures.

In operation, the heat transfer system 200 can be used to maintain adesired condition in the interior space 150 of the transport unit 125.More particularly, the first heat transfer circuit 205 may receive heatthat is rejected from the second heat transfer circuit 210 via thecascade heat exchanger 255. The second heat transfer circuit 210 can inturn be used to maintain the desired condition within the interior space150.

The first heat transfer circuit 205 can function according to generallyknown principles in order to remove heat from the second heat transfercircuit 210. The compressor 220 compresses the heat transfer fluid froma relatively lower pressure gas to a relatively higher-pressure gas. Therelatively higher-pressure gas is discharged from the compressor 220 andflows through the condenser 230. In accordance with generally knownprinciples, the heat transfer fluid flows through the condenser 230 andrejects heat to a heat transfer fluid or medium (e.g., air, etc.),thereby cooling the heat transfer fluid or medium. The condenser fan235, in accordance with generally known principles, can aid in removingthe heat from the heat transfer fluid in the first heat transfer circuit205. The cooled heat transfer medium which is now in a liquid form flowsthrough the heat exchanger 245 where the heat transfer fluid is furthersub-cooled prior to entering the expansion device 250. The heatexchanger 245 may alternatively be referred to as the suction-to-liquidline heat exchanger 245. The heat exchanger 245 can further sub-cool theheat transfer fluid which can, in an embodiment, increase a capacity ofthe first heat transfer circuit 205. The heat transfer fluid, in a mixedliquid and gaseous form, flows to the cascade heat exchanger 255.

At the cascade heat exchanger 255, the heat transfer medium in the firstheat transfer circuit 205 absorbs heat from the heat transfer medium ofthe second heat transfer circuit 210, heating the heat transfer fluidand converting it to a gaseous form. The gaseous heat transfer fluidthen flows through the second accumulator 260 and returns to thecompressor 220. The above-described process can continue while the heattransfer circuit 205 is operating (e.g., when the prime mover 215 isoperating). In an embodiment, the cascade heat exchanger 255 and theheat exchange relationship between the first heat transfer circuit 205and the second heat transfer circuit 210 can increase an efficiency ofthe refrigeration system by, for example, reducing an amount of energyinput via the power source 215 to maintain the one or more desiredconditions inside the transport unit 125 (FIG. 1). In an embodiment, thereduction in energy input can, for example, reduce an impact on theenvironment. In an embodiment, the cascade heat exchanger 255 can reduceuse of high pressure refrigeration components (e.g., by enabling use oflower pressure heat transfer fluids).

The second heat transfer circuit 210 can function according to generallyknown principles in order to reject heat to the first heat transfercircuit 205. The second compressor 275 compresses the heat transferfluid from a relatively lower pressure gas to a relativelyhigher-pressure gas. The relatively higher-pressure gas is dischargedfrom the second compressor 275 and flows through the cascade heatexchanger 255. In accordance with generally known principles, the heattransfer fluid can be in a heat exchange relationship with the heattransfer fluid of the first heat transfer circuit 205 condenser 230 andcan reject heat to the heat transfer fluid of the first heat transfercircuit 205, thereby cooling the heat transfer fluid of the second heattransfer circuit 210. The cooled heat transfer medium which is now in aliquid form can flow through the third accumulator 280 to the secondexpansion device 285. As a result, a portion of the heat transfer fluidis converted to a gaseous form. The heat transfer fluid, which is now ina mixed liquid and gaseous form, can flow to the evaporator 290. At theevaporator 290, the heat transfer medium in the second heat transfercircuit 210 can absorb heat from a heat transfer medium (e.g., air),heating the heat transfer fluid and converting it to a gaseous form. Theevaporator fan 295, in accordance with generally known principles, canaid in absorbing the heat from the heat transfer fluid in the secondheat transfer circuit 210. The evaporator fan 295 can also, for example,blow air into the conditioned space 150 in order to maintain the desiredcondition. The gaseous heat transfer fluid can then return to thecompressor 220. The above-described process can continue while the heattransfer circuit 210 is operating.

FIG. 3A is a schematic diagram of a heat transfer circuit 300 which canbe included in place of the heat transfer circuit 210 (FIG. 2) in theheat transfer system 200 (FIG. 2), according to an embodiment. The heattransfer circuit 300 additionally includes a flow control device 305.The flow control device 305 can be, for example, a four-way valve, orthe like. In operation, the flow control device 305 can be used tomodify the flow of the heat transfer fluid in the heat transfer circuit300. This can, for example, enable the heat transfer circuit to be usedin a cooling mode (e.g., the second heat transfer circuit 210 asdescribed in accordance with FIG. 2 above) or in a heating mode, inwhich the flow of the heat transfer fluid is reversed in order to rejectheat to the conditioned space 150 (FIG. 1) instead of rejecting heatfrom the conditioned space 150.

FIG. 3B is a schematic diagram of a heat transfer circuit 310 which canbe included in place of the heat transfer circuit 210 (FIG. 2) in theheat transfer system 200 (FIG. 2), according to an embodiment. The heattransfer circuit 310 additionally includes a hot-gas bypass flow 315 anda flow control device 320. The hot-gas bypass flow 315 can be used, forexample, to divert a portion of heat transfer fluid to defrost theevaporator 290. The flow control device 320 can be, for example, asolenoid valve (or similar type of valve) which either enables ordisables flow of the heat transfer fluid. In an embodiment, the flowcontrol device 320 can have one or more intermediate positions in whichflow of the heat transfer fluid therethrough is partially enabled.

FIG. 4A is a schematic diagram of a heat transfer system 400A for a TRS(e.g., the TRS 100 of FIG. 1), according to an embodiment. The heattransfer system 400A includes a first heat transfer circuit 405A and asecond heat transfer circuit 410A. In an embodiment, the first heattransfer circuit 405A can alternatively be referred to as the primaryheat transfer circuit 405A, the high side heat transfer circuit 405A,the condensing side heat transfer circuit 405A, the stage two heattransfer circuit 405A, or the like. In an embodiment, the second heattransfer circuit 410A can alternatively be referred to as the low sideheat transfer circuit 410A, the evaporating side heat transfer circuit410A, or the like. The first heat transfer circuit 405A is in thermalcommunication with the second heat transfer circuit 410A. Aspects of theheat transfer circuit 410A may be optional, as illustrated in dashedlines in the figure.

Aspects of the heat transfer system 400A may be the same as or similarto aspects of the heat transfer system 200 of FIG. 2.

The first heat transfer circuit 405A includes a compressor 415A, acondenser 420A, an expansion device 425A, and a cascade heat exchanger430A. It will be appreciated that the first heat transfer circuit 405Acan include one or more additional components. For example, the firstheat transfer circuit 405A can include one or more of the componentsshown and described in accordance with FIG. 4B below.

The compressor 415A, condenser 420A, expansion device 425A, and cascadeheat exchanger 430A are fluidly connected to form the first heattransfer circuit 405A in which a heat transfer fluid can circulatetherethrough. The heat transfer fluid can generally be a heat transferfluid having a relatively low global warming potential (GWP). Examplesof suitable heat transfer fluids for the first heat transfer circuit405A can include, but are not limited to, hydrofluoroolefins (HFOs),hydrocarbons (HCs), and carbon dioxide (CO₂) (also known by its ASHRAEStandard 34 designation R-744), or the like.

The second heat transfer circuit 410A includes a compressor 435A, anexpansion device 440A, and an evaporator 445A. The compressor 435A,cascade heat exchanger 430A, expansion device 440A, and evaporator 445Aare fluidly connected to form the second heat transfer circuit 410A inwhich a heat transfer fluid can circulate therethrough. The heattransfer fluid can generally be a heat transfer fluid having arelatively low global warming potential (GWP). Examples of suitable heattransfer fluids for the second heat transfer circuit 410A can include,but are not limited to, hydrofluoroolefins (HFOs), hydrocarbons (HCs),and carbon dioxide (CO₂) (also known by its ASHRAE Standard 34designation R-744), or the like. In an embodiment, the heat transferfluid in the first heat transfer circuit 405A and the heat transferfluid for the second heat transfer circuit 410A can be the same. In anembodiment, the heat transfer fluid in the first heat transfer circuit405A and the heat transfer fluid for the second heat transfer circuit410A can be different.

The second heat transfer circuit 410A can include one or more additionalcomponents. For example, in an embodiment, the second heat transfercircuit 410A includes one or more of an intercooler 450A, asuction-liquid heat exchanger 455A, an expansion device 460A, and aneconomizer 465A. In an embodiment, the economizer 465A can include aneconomizer heat exchanger. In an embodiment, the economizer 465A caninclude a flash tank economizer.

In an embodiment, a location of the suction-liquid heat exchanger 455Aand the economizer 465A can be switched. That is, in the illustratedembodiment, the suction-liquid heat exchanger 455A is disposed betweenthe economizer 465A and the cascade heat exchanger 430A. In anembodiment, the economizer 465A can be disposed between thesuction-liquid heat exchanger 455A and the cascade heat exchanger 430A.In an embodiment, the one or more additional components can, forexample, increase an efficiency of the heat transfer system 400A. In anembodiment, the one or more additional components can, for example,reduce a size of the cascade heat exchanger 430A.

The compressors 415A and 435A can be driven by a power source (e.g., thepower source 215 in FIG. 2) (not shown in FIG. 4A).

In operation, the heat transfer system 400A can be used to maintain adesired condition in the interior space 150 of the transport unit 125.More particularly, the first heat transfer circuit 405A may receive heatthat is rejected from the second heat transfer circuit 410A via thecascade heat exchanger 430A. The second heat transfer circuit 410A canin turn be used to maintain the desired condition within the interiorspace 150.

FIG. 4B is a schematic diagram of a heat transfer system 400B for a TRS(e.g., the TRS 100 of FIG. 1), according to an embodiment. The heattransfer system 400B includes a first heat transfer circuit 405B and asecond heat transfer circuit 410B. In an embodiment, the first heattransfer circuit 405B can alternatively be referred to as the primaryheat transfer circuit 405B, the high side heat transfer circuit 405B,the condensing side heat transfer circuit 405B, the stage two heattransfer circuit 405B, or the like. In an embodiment, the second heattransfer circuit 410B can alternatively be referred to as the low sideheat transfer circuit 410B, the evaporating side heat transfer circuit410B, or the like. The first heat transfer circuit 405B is in thermalcommunication with the second heat transfer circuit 410B. Aspects of theheat transfer circuit 405B may be optional, as illustrated in dashedlines in the figure.

Aspects of the heat transfer system 400B may be the same as or similarto aspects of the heat transfer system 200 of FIG. 2.

The first heat transfer circuit 405B includes a compressor 415B, acondenser 420B, an expansion device 425B, and a cascade heat exchanger430B.

The compressor 415B, condenser 420B, expansion device 425B, and cascadeheat exchanger 430B are fluidly connected to form the first heattransfer circuit 405B in which a heat transfer fluid can circulatetherethrough. The heat transfer fluid can generally be a heat transferfluid having a relatively low global warming potential (GWP). Examplesof suitable heat transfer fluids for the first heat transfer circuit405B can include, but are not limited to, hydrofluoroolefins (HFOs),hydrocarbons (HCs), and carbon dioxide (CO₂) (also known by its ASHRAEStandard 34 designation R-744), or the like.

The first heat transfer circuit 405B can include one or more additionalcomponents. For example, in an embodiment, the first heat transfercircuit 405B includes one or more of a suction-liquid heat exchanger470B, an economizer 475B, and an expansion device 480B. In anembodiment, the economizer 475B can include an economizer heatexchanger. In an embodiment, the economizer 475B can include a flashtank economizer. In an embodiment, the one or more additional componentscan, for example, increase an efficiency of the first heat transfercircuit 405B, and accordingly, the heat transfer system 400B.

The second heat transfer circuit 410B includes a compressor 435B, anexpansion device 440B, and an evaporator 445B. It will be appreciatedthat the second heat transfer circuit 410B can include one or moreadditional components. For example, the second heat transfer circuit410B can include one or more of the components shown and described inaccordance with FIG. 4A above.

The compressor 435B, cascade heat exchanger 430B, expansion device 440B,and evaporator 445B are fluidly connected to form the second heattransfer circuit 410B in which a heat transfer fluid can circulatetherethrough. The heat transfer fluid can generally be a heat transferfluid having a relatively low global warming potential (GWP). Examplesof suitable heat transfer fluids for the second heat transfer circuit410B can include, but are not limited to, hydrofluoroolefins (HFOs),hydrocarbons (HCs), and carbon dioxide (CO₂) (also known by its ASHRAEStandard 34 designation R-744), or the like. In an embodiment, the heattransfer fluid in the first heat transfer circuit 405B and the heattransfer fluid for the second heat transfer circuit 410B can be thesame. In an embodiment, the heat transfer fluid in the first heattransfer circuit 405B and the heat transfer fluid for the second heattransfer circuit 410B can be different.

The compressors 415B, 435B can be driven by a power source (e.g., thepower source 215 in FIG. 2) (not shown in FIG. 4B).

In operation, the heat transfer system 400B can be used to maintain adesired condition in the interior space 150 of the transport unit 125.More particularly, the first heat transfer circuit 405B may receive heatthat is rejected from the second heat transfer circuit 410B via thecascade heat exchanger 430B. The second heat transfer circuit 410B canin turn be used to maintain the desired condition within the interiorspace 150.

It is to be appreciated that aspects of FIGS. 4A and 4B can be combined.For example, a heat transfer system can include the first heat transfercircuit 405A and the second heat transfer circuit 410B. In anembodiment, a heat transfer system can include the first heat transfercircuit 405B and the second heat transfer circuit 410A.

Aspects:

It is noted that any one of aspects 1-12 below can be combined with anyone of aspects 13-23, 24-26, and/or 27-28. Any one of aspects 13-23 canbe combined with any one of aspects 24-26 and/or 27-28. Any one ofaspects 24-26 can be combined with any one of aspects 27-28.

Aspect 1. A transport refrigeration system (TRS), comprising:

a first heat transfer circuit, including:

-   -   a first compressor, a condenser, a first expansion device, and a        cascade heat exchanger, wherein the first compressor, the        condenser, the first expansion device, and the cascade heat        exchanger are in fluid communication such that a first heat        transfer fluid can flow therethrough; and

a second heat transfer circuit, including:

-   -   a second compressor, the cascade heat exchanger, a second        expansion device, and an evaporator, wherein the second        compressor, the cascade heat exchanger, the second expansion        device, and the evaporator are in fluid communication such that        a second heat transfer fluid can flow therethrough;

wherein the first heat transfer circuit and the second heat transfercircuit are arranged in thermal communication at the cascade heatexchanger such that the first heat transfer fluid and the second heattransfer fluid are in a heat exchange relationship at the cascade heatexchanger.

Aspect 2. The TRS according to aspect 1, further comprising a primemover configured to provide mechanical power to the first compressor.

Aspect 3. The TRS according to aspect 2, further comprising a generatorconnected to the prime mover such that the prime mover providesmechanical power to the generator, wherein the generator is electricallyconnected to the second compressor to provide an electric power to thesecond compressor.

Aspect 4. The TRS according to any one of aspects 1-3, wherein the firstheat transfer fluid and the second heat transfer fluid are different.

Aspect 5. The TRS according to any one of aspects 1-4, wherein the firstheat transfer fluid has a relatively low global warming potential (GWP).

Aspect 6. The TRS according to aspect 5, wherein the first heat transferfluid is an unsaturated hydrofluorocarbon (HFC).

Aspect 7. The TRS according to aspect 6, wherein the first heat transferfluid is one of a hydrofluoroolefin (HFO), a hydrocarbon (HC), ammonia,or carbon dioxide (CO₂).

Aspect 8. The TRS according to any one of aspects 1-7, wherein thesecond heat transfer fluid is carbon dioxide (CO₂).

Aspect 9. The TRS according to any one of aspects 1-8, wherein thesecond heat transfer circuit further includes a four-way flow controldevice.

Aspect 10. The TRS according to any one of aspects 1-9, wherein thesecond heat transfer circuit further includes a hot-gas bypass.

Aspect 11. The TRS according to any one of aspects 1-10, wherein thesecond heat transfer circuit further includes one or more of anintercooler, a suction-liquid heat exchanger, and an economizer.

Aspect 12. The TRS according to any one of aspects 1-11, wherein thefirst heat transfer circuit further includes one or more of asuction-liquid heat exchanger and an economizer.

Aspect 13. A system, comprising:

an internal combustion engine;

a first heat transfer circuit, including:

-   -   a first compressor, a condenser, a first expansion device, and a        cascade heat exchanger, wherein the first compressor, the        condenser, the first expansion device, and the cascade heat        exchanger are in fluid communication such that a first heat        transfer fluid can flow therethrough; and

a second heat transfer circuit, including:

-   -   a second compressor, the cascade heat exchanger, a second        expansion device, and an evaporator, wherein the second        compressor, the cascade heat exchanger, the second expansion        device, and the evaporator are in fluid communication such that        a second heat transfer fluid can flow therethrough;

wherein the first heat transfer circuit and the second heat transfercircuit are arranged in thermal communication at the cascade heatexchanger such that the first heat transfer fluid and the second heattransfer fluid are in a heat exchange relationship at the cascade heatexchanger.

Aspect 14. The system according to aspect 13, further comprising agenerator coupled to the internal combustion engine, wherein thegenerator is configured to provide an electrical power to the secondcompressor.

Aspect 15. The system according to any one of aspects 13-14, wherein thefirst heat transfer fluid and the second heat transfer fluid aredifferent.

Aspect 16. The system according to any one of aspects 13-15, wherein thefirst heat transfer fluid has a relatively low global warming potential(GWP).

Aspect 17. The system according to aspect 16, wherein the first heattransfer fluid is an unsaturated hydrofluorocarbon (HFC).

Aspect 18. The system according to aspect 17, wherein the first heattransfer fluid is one of a hydrofluoroolefin (HFO), a hydrocarbon (HC),ammonia, or carbon dioxide (CO₂).

Aspect 19. The system according to any one of aspects 13-18, wherein thesecond heat transfer fluid is carbon dioxide (CO₂).

Aspect 20. The system according to any one of aspects 13-19, wherein thesecond heat transfer circuit further includes a four-way flow controldevice.

Aspect 21. The system according to any one of aspects 13-20, wherein thesecond heat transfer circuit further includes a hot-gas bypass.

Aspect 22. The system according to any one of aspects 13-21, wherein thesecond heat transfer circuit further includes one or more of anintercooler, a suction-liquid heat exchanger, and an economizer.

Aspect 23. The system according to any one of aspects 13-22, wherein thefirst heat transfer circuit further includes one or more of asuction-liquid heat exchanger and an economizer.

Aspect 24. A method of heat transfer in a transport refrigeration system(TRS), the TRS having a first heat transfer circuit and a second heattransfer circuit in thermal communication via a cascade heat exchanger,the method comprising:

circulating a first heat transfer fluid through the first heat transfercircuit;

circulating a second heat transfer fluid through the second heattransfer circuit; and

exchanging heat between the first heat transfer fluid and the secondheat transfer fluid via the cascade heat exchanger.

Aspect 25. The method according to aspect 24, wherein exchanging heatbetween the first heat transfer fluid and the second heat transfer fluidvia the cascade heat exchanger includes rejecting heat from the secondheat transfer fluid to the first heat transfer fluid.

Aspect 26. The method according to aspect 25, wherein the second heattransfer circuit is in thermal communication with a conditioned space ofthe TRS, and the method further includes controlling one or moreenvironmental conditions in the conditioned space with the second heattransfer circuit.

Aspect 27. A transport refrigeration system (TRS), comprising:

a first heat transfer circuit, including:

-   -   a first compressor, a condenser, a first expansion device, an        economizer, a second expansion device, and a cascade heat        exchanger, wherein the first compressor, the condenser, the        first expansion device, the economizer, the second expansion        device, and the cascade heat exchanger are in fluid        communication such that a first heat transfer fluid can flow        therethrough; and

a second heat transfer circuit, including:

-   -   a second compressor, an intercooler, the cascade heat exchanger,        a suction-liquid heat exchanger, a third expansion device, and        an evaporator, wherein the second compressor, the intercooler,        the cascade heat exchanger, the suction-liquid heat exchanger,        the third expansion device, and the evaporator are in fluid        communication such that a second heat transfer fluid can flow        therethrough;

wherein the first heat transfer circuit and the second heat transfercircuit are arranged in thermal communication at the cascade heatexchanger such that the first heat transfer fluid and the second heattransfer fluid are in a heat exchange relationship at the cascade heatexchanger.

Aspect 28. The TRS according to aspect 27, wherein the economizer is oneof an economizer heat exchanger and a flash tank economizer.

The terminology used in this specification is intended to describeparticular embodiments and is not intended to be limiting. The terms“a,” “an,” and “the” include the plural forms as well, unless clearlyindicated otherwise. The terms “comprises” and/or “comprising,” whenused in this specification, specify the presence of the stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, and/or components.

With regard to the preceding description, it is to be understood thatchanges may be made in detail, especially in matters of the constructionmaterials employed and the shape, size, and arrangement of parts withoutdeparting from the scope of the present disclosure. This specificationand the embodiments described are exemplary only, with the true scopeand spirit of the disclosure being indicated by the claims that follow.

What is claimed is:
 1. A transport refrigeration system (TRS),comprising: a first heat transfer circuit, including: a firstcompressor, a condenser, a first expansion device, and a cascade heatexchanger, wherein the first compressor, the condenser, the firstexpansion device, and the cascade heat exchanger are in fluidcommunication such that a first heat transfer fluid can flowtherethrough; and a second heat transfer circuit, including: the cascadeheat exchanger, and an evaporator, wherein the cascade heat exchangerand the evaporator are in fluid communication such that a second heattransfer fluid can flow therethrough; wherein the first heat transfercircuit and the second heat transfer circuit are arranged in thermalcommunication at the cascade heat exchanger such that the first heattransfer fluid and the second heat transfer fluid are in a heat exchangerelationship at the cascade heat exchanger, wherein the transportrefrigeration system is configured to control one or more environmentalconditions within a conditioned space of a transport unit, wherein thefirst heat transfer circuit is configured such that the first heattransfer fluid is directed from the first compressor directly to thecondenser, and wherein the first heat transfer fluid and the second heattransfer fluid are different heat transfer fluids.
 2. The TRS accordingto claim 1, further comprising an engine configured to providemechanical power to the first compressor.
 3. The TRS according to claim1, wherein the first heat transfer fluid has a relatively low globalwarming potential (GWP).
 4. The TRS according to claim 3, wherein thefirst heat transfer fluid is one of an unsaturated hydrofluorocarbon(HFC), a hydrofluoroolefin (HFO), a hydrocarbon (HC), ammonia, or carbondioxide (CO₂).
 5. The TRS according to claim 1, wherein the second heattransfer fluid is carbon dioxide (CO₂).
 6. The TRS according to claim 1,wherein the first heat transfer circuit includes one or more of asuction-liquid heat exchanger and an economizer.
 7. The TRS according toclaim 1, wherein the evaporator of the second heat transfer circuit isin thermal communication with the conditioned space.
 8. The transportrefrigeration system of claim 1, wherein the second heat transfercircuit further includes one or more of a hot-gas bypass, anintercooler, a suction-liquid heat exchanger, and an economizer.
 9. Thetransport refrigeration system of claim 5, wherein the first heattransfer circuit and the second heat transfer circuit are separatecircuits such that the first heat transfer fluid is fluidly isolatedfrom the second heat transfer fluid.
 10. A system, comprising: a firstheat transfer circuit, including: a first compressor, a condenser, afirst expansion device, and a cascade heat exchanger, wherein the firstcompressor, the condenser, the first expansion device, and the cascadeheat exchanger are in fluid communication such that a first heattransfer fluid can flow therethrough; and a second heat transfercircuit, including: the cascade heat exchanger and an evaporator,wherein the cascade heat exchanger and the evaporator are in fluidcommunication such that a second heat transfer fluid can flowtherethrough; wherein the first heat transfer circuit and the secondheat transfer circuit are arranged in thermal communication at thecascade heat exchanger such that the first heat transfer fluid and thesecond heat transfer fluid are in a heat exchange relationship at thecascade heat exchanger, wherein the first heat transfer circuit isconfigured such that the first heat transfer fluid is directed from thefirst compressor directly to the condenser, and wherein the first heattransfer fluid and the second heat transfer fluid are different heattransfer fluids.
 11. The system according to claim 10, wherein the firstheat transfer fluid has a relatively low global warming potential (GWP).12. The system according to claim 11, wherein the first heat transferfluid is one of an unsaturated hydrofluorocarbon (HFC), ahydrofluoroolefin (HFO), a hydrocarbon (HC), ammonia, or carbon dioxide(CO₂).
 13. The system according to claim 10, wherein the second heattransfer fluid is carbon dioxide (CO₂).
 14. The system according toclaim 10, wherein the first heat transfer circuit further includes oneor more of a suction-liquid heat exchanger and an economizer.
 15. Thesystem according to claim 10, wherein the evaporator of the second heattransfer circuit is in thermal communication with a conditioned space.16. The system of claim 10, wherein the second heat transfer circuitfurther includes one or more of a hot-gas bypass, an intercooler, asuction-liquid heat exchanger, and an economizer.
 17. The system ofclaim 10, wherein the first heat transfer circuit and the second heattransfer circuit are separate circuits such that the first heat transferfluid is fluidly isolated from the second heat transfer fluid.
 18. Amethod of heat transfer in a transport refrigeration system (TRS), theTRS having a first heat transfer circuit and a second heat transfercircuit in thermal communication via a cascade heat exchanger, themethod comprising: circulating a first heat transfer fluid through thefirst heat transfer circuit, wherein circulating the first heat transferfluid through the first heat transfer circuit includes directing thefirst heat transfer fluid from a first compressor directly to acondenser; circulating a second heat transfer fluid through the secondheat transfer circuit; and exchanging heat between the first heattransfer fluid and the second heat transfer fluid via the cascade heatexchanger, wherein the first heat transfer fluid and the second heattransfer fluid are different heat transfer fluids.
 19. The methodaccording to claim 18, wherein exchanging heat between the first heattransfer fluid and the second heat transfer fluid via the cascade heatexchanger includes rejecting heat from the second heat transfer fluid tothe first heat transfer fluid.
 20. The method according to claim 18,wherein the second heat transfer circuit is in thermal communicationwith a conditioned space of a transport unit provided climate control bythe TRS, and the method further includes controlling one or moreenvironmental conditions in the conditioned space with the second heattransfer circuit.
 21. The method of claim 18, further comprisingexchanging heat between an evaporator in the second heat transfercircuit and the conditioned space.